The subject of the present invention is a component arrangement, preferably an electronic component arrangement, having a first substrate and at least one second substrate which is disposed on the first substrate, e.g. an electronic component, such as an unhoused integrated circuit or similar, the first substrate having at least one first contact element and the at least one electronic component having at least one second contact element and the contact elements which are connected to each other to form an electrical contacting and each contact element having a contact surface, and the component arrangement having furthermore a support layer which connects the first substrate and the at least one second substrate, and also a method for production of such a component arrangement.
In the case of flip-chip assembly, an electronic component is mounted with its contact terminals towards a substrate, the contact elements of the component being contacted respectively with the oppositely situated contact elements of the substrate. As a result, an electrical contacting is produced which connects the substrate to the electronic component conductively to form an electronic component arrangement. Between the electronic component and the substrate there remains however a gap and there are often compelling reasons for filling the gap between the component and the substrate.
By filling the gap, the mechanical stability of the electronic component arrangement can be improved since, in the case of temperature changes and the thereby occurring mechanical stresses due to the different coefficients of expansion between substrate and electronic component element, the filling relieves the load on the electrical contactings. Furthermore, penetration of particles and liquids into the gap is prevented and consequently possible short circuits or corrosion are avoided. Protection by a filling is required at the latest during sawing or separation of the substrates or later under operating conditions. Such substrates can be for example silicon wafers, a laminate or a glass, on which an electronic component, such as an unhoused IC component or even a further substrate is mounted.
In prior art, generally a so-called encapsulation compound is used, also termed underfiller. The underfiller is generally a polymer which is deposited directly next to the chip and is drawn into the gap as a result of capillary forces. Subsequently, the underfiller is cured at fairly high temperatures. The underfiller is filled with particles in order to lower the thermal coefficient of expansion of the polymer and to reduce the mechanical stresses. In addition to the long process times for filling the gap, also the requirement for sufficient space next to the gap is disadvantageous in the use of underfillers since the liquid polymer material must be deposited there and possibly must be relaid several times in order to provide the necessary volume for filling the gap.
For this reason, a method has been developed in which firstly the underfiller is applied and subsequently the electronic component with for example solder bumps as contact elements is pressed into the liquid underfiller until the solder bumps reach the contact elements of the substrate, melt and produce the electrical contacting. At the same time, the underfiller is cured. For this purpose, supplements must be added which promote wetting in the underfiller in order to reduce the oxides and for protection from renewed oxidation during the soldering. Underfillers of this type cannot however be filled sufficiently and hence the thermal coefficient of expansion is not adequately lowered. In addition, the assembly of the electronic component on the substrate is relatively difficult: thus the individual electronic components must be pressed onto the substrate with a tool during bonding in order to avoid floating and hence a loss of electronic contact. However, too strong pressure forces lead to the solder being pressed out of a solder bump and electrical short circuits between the contacts. A further disadvantage of the above-described method is the high tendency for pore formation in the underfiller, which further reduces the reliability.
Another possibility for circumventing the introduction of an underfiller after production of the electrical contacting between the electronic component and the substrate is associated with flip-chip assembly by means of gluing. There are two method variants here: firstly, gluing with unfilled adhesives (non-conductive adhesive, NCA) and, on the other hand, the use of anisotropically conductive adhesives (anisotropic conductive adhesive, ACA). In both cases, gold bumps are generally applied on the chip side as contact elements, the adhesive is applied on the substrate side, and the non-melting bumps of the chip are pressed into the liquid adhesive with a hot tool, the adhesive completely wetting the chip surface and curing. In the case of the NCA variant, a gold bump is pressed against the terminal contact on the substrate side. The adhesive shrinks during curing of the adhesive and produces a permanent pressure contact between the bump and the substrate terminal. In the case of the ACA variant, small conductive particles with almost the same diameter are contained in the adhesive, the particles being jammed between the gold bump and the substrate terminal and ensuring the electrical contact after curing.
A third variant for the assembly of chips on wafers is proposed by the Interuniversity Microelectronics Centre (IMEC). In the proposed process, firstly a thin polymer layer is applied on the wafer and subsequently the electric component, provided with copper bumps, is placed on the adhesive. With the help of a tool, the chips are pressed against the wafer finally with application of temperature and pressure (thermocompression), the polymer layer melting, the copper bumps displacing the polymer locally and being welded with an oppositely situated copper pad which is applied on the substrate as contact element. Since however copper can only be welded with difficulty, inadequate contact must be accepted, which is sustained by the shrinkage and the curing of the polymer.